大型电力变压器铁芯剩磁测试与削弱

During the closing process for large power transformer, the inrush current could be produced as the existence of iron core remanence, which will prevent the transformer to operate in power grid, therefore the power supply continuity will be influenced. This project focuses on investigating the test method for iron core remanence magnitude and direction, and the optimal method for remanence weakening. Firstly, DC voltages with same magnitude but opposite directions are applied to the winding which is wound on the closed iron core ring respectively, so two currents with the different waveforms will be induced in winding as the existence iron core remanence. The remanence magnitude and direction will be obtained based on the difference of these two currents and the field-circuit coupled transient analysis method. Secondly, in order to improve the accuracy of the remanence test method, the suitable magnitude of the DC voltage will be obtained by theoretical analysis and test verification. For calculating the remanence, the storage and value read method of the transient current caused by the DC voltage will be studied. Based on the determined remanence magnitude and direction, the high efficient remanence weakening method will be studied. Lastly, the device for remanence test and weakening will be developed. The principle and method used in this project will be verified with the experiment on a 220 kV power transformer. The work done in the project will be significant to eliminating the inrush current in the power transformer, and has important application value for the high efficient operation of power grid.

进行大型电力变压器合闸操作时，铁芯中的剩磁可能会引起励磁涌流、导致变压器不能再投入运行，进而影响电网供电的连续性。本课题旨在测试铁芯剩磁大小和方向，并寻求合适的剩磁削弱方法。首先，在一封闭环形铁芯绕组上先后分别施加大小相等方向相反的直流电压，铁芯剩磁的存在使得绕组中出现两次波形不同的电流，据此不同并结合场路暂态分析，推断出铁芯剩磁的大小和方向。其次，为提高剩磁测试的准确性，通过理论分析和试验验证确定直流电压的合适区间；研究暂态电流波形的存储和电流值的读取，以便计算剩磁大小；在已知剩磁大小和方向的基础上，研究高效的剩磁削弱方法。最后，研制出一套完整的剩磁测试与削弱装置，并以一台220kV变压器绕组剩磁作为实例，验证铁芯剩磁测试与削弱方法的有效性。本课题研究成功将对消除变压器励磁涌流问题具有重要理论意义，对电网高效运行具有重要应用价值。

随着电力技术与超高压电网的不断发展，大容量电力变压器在电网中的应用日益增多，这对电力设备的运行提出了更高要求。电力变压器在进行各种检测试验后，由于铁磁材料的磁滞特性，变压器铁芯中通常会残留一定的剩磁。变压器空载合闸且合闸相角不合适时，剩磁导致的励磁涌流会对电力变压器的继电保护装置以及其它设备造成诸多不利影响。准确测量大型电力变压器铁芯剩磁并采取适当的剩磁削弱方案，对大型电力变压器乃至电网高效运行具有重要的理论意义与实际应用价值。本项目对大型电力变压器剩磁测量与削弱问题进行了研究，主要创新工作如下：.（1）提出了一种对铁芯绕组外施正、反向直流电压激励的剩磁测量方法，结合场路耦合分析，建立了变压器铁芯内剩磁与可测量参数的关系，并通过有限元方法获得测量剩磁的经验公式。该方法能够准确测量铁芯内剩磁同时不对变压器作任何要求；.（2）针对铁芯材料局部剩磁特性进行了大量的测量实验，并深入研究铁芯材料的剩磁特性。通过采用测量得到的局部BH曲线进行仿真计算，提高了仿真计算结果的准确性；.（3）针对铁芯内剩磁削弱的问题，在准确测量变压器铁芯剩磁的基础上，提出了一种一次性削弱铁芯剩磁的方法，此方法能够高效地削弱变压器铁芯内剩磁；.（4）研制一套以DSP为核心的暂态电流测量系统，解决了剩磁测量过程中信号采集和数据处理的问题，并在此基础上设计了一种测量和削弱变压器剩磁的装置，使得提出方法能够应用于现场工作的变压器。